Scalar interfaces in the near field of a unity velocity ratio coaxial jet

Planar laser-induced fluorescence is employed to investigate the concentration field in the developing region of a coaxial jet with an annular to inner jet velocity of one. Seeding the annular flow with a scalar shows that prior to the erosion of the inner scalar core, an inner interface exists, across which the scalar quantities exhibit sharp gradients akin to the traditional outer interface. Coarse grain filtering revealed that the outer interface establishes the universal fractal scaling before the onset of self-similarity, while the inner interface does not develop sufficient scale separation to do so due to the lack of shear.